.. PRTG Manual: SNMP Custom String Sensor

The SNMP Custom String sensor monitors a string returned by a specific object identifier (OID) using the Simple Network Management Protocol (SNMP). It can check for keywords. If you want to set limits to the channel value, you can also extract a numeric value contained in the string.

The sensor can show the following:

Response time of the monitored device

A value extracted from the string (optionally)

In the sensor message, the sensor shows the string you search for and the reason for a current Warning or Downstatus.

It might not work to query data from a probe device via SNMP (querying localhost, 127.0.0.1, or ::1). Add this device to PRTG with the IP address that it has in your network and create the SNMP sensor on this device instead.

The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the setting fields that are required for creating the sensor. Therefore, you do not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.

Sensor Settings

Click the Settings tab of a sensor to change its settings.

Usually, a sensor connects to the IP Address or DNS Name of the parent device on which you created the sensor. See the device settings for details. For some sensors, you can explicitly define the monitoring target in the sensor settings. See below for details on available settings.

Enter one or more tags, separated by spaces or commas. You can use tags to group sensors and use tag–filtered views later on. Tags are not case sensitive. We recommend that you use the default value.

There are default tags that are automatically predefined in a sensor's settings when you add a sensor. See section Default Tags below.

You can add additional tags to the sensor if you like. Other tags are automatically inherited from objects further up in the device tree. These are visible above as Parent Tags.

It is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with parentheses (()) or angle brackets (<>).

Priority

Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. A sensor with a top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority).

Default Tags

snmpcustomstringsensor

OID Settings

OID

Enter the OID of the SNMP object that you want to receive a string from.

Most OIDs begin with 1.3.6.1. However, entering OIDs starting with 1.0, or 1.1, or 1.2 is also allowed. If you want to entirely disable the validation of your entry, add the string norfccheck: at the beginning of your OID, for example, norfccheck:2.0.0.0.1.

Maximum Length of String

Define the maximum allowed length of the string that PRTG receives from the SNMP object at the specified OID. If the string is longer than this value, the sensor shows a Downstatus. Enter an integer value or leave the field empty.

If Value Changes

Define what the sensor does when the sensor value changes:

Ignore changes (default): Take no action on change.

Trigger 'change' notification: Send an internal message indicating that the sensor value has changed. In combination with a change trigger, you can use this mechanism to trigger a notification whenever the sensor value changes.

Keyword Search

Response Must Include (Down Status)

Define the search string that must be part of the data that PRTG receives from the SNMP object at the specified OID. You can enter a simple string in plain text or a regular expression.

The search string must be case sensitive.

If the data does not include the search pattern, the sensor shows a Downstatus.

Search Method

Define the method with which you want to provide the search string.

Simple string search: Search for a simple string in plain text.The characters * and ? work as placeholders. * stands for no number or any number of characters and ? stands for exactly one character (as known from the Windows search). This behavior cannot be disabled, so the literal search for these characters is only possible using a regular expression.

Define the search string that must not be part of the data that PRTG receives form the SNMP object at the specified OID. You can enter a simple string in plain text or a regular expression.

The search string must be case sensitive.

If the data does include the search pattern, the sensor shows a Downstatus.

Search Method

Define the method with which you want to provide the search string.

Simple string search: Search for a simple string in plain text.The characters * and ? work as placeholders. * stands for no number or any number of characters and ? stands for exactly one character (as known from the Windows search). This behavior cannot be disabled, so the literal search for these characters is only possible using a regular expression.

Define the search string that must be part of the data that PRTG receives from the SNMP object at the specified OID. You can enter a simple string in plain text or a regular expression.

The search string must be case sensitive.

If the data does not include the search pattern, the sensor shows a Warningstatus.

Search Method

Define the method with which you want to provide the search string.

Simple string search: Search for a simple string in plain text.The characters * and ? work as placeholders. * stands for no number or any number of characters and ? stands for exactly one character (as known from the Windows search). This behavior cannot be disabled, so the literal search for these characters is only possible using a regular expression.

Define the search string that must not be part of the data that PRTG receives form the SNMP object at the specified OID. You can enter a simple string in plain text or a regular expression.

The search string must be case sensitive.

If the data does include the search pattern, the sensor shows a Warningstatus.

Search Method

Define the method with which you want to provide the search string.

Simple string search: Search for a simple string in plain text.The characters * and ? work as placeholders. * stands for no number or any number of characters and ? stands for exactly one character (as known from the Windows search). This behavior cannot be disabled, so the literal search for these characters is only possible using a regular expression.

No extraction: Do not extract a float value. Use the result as a string value.

Extract a numeric value using a regular expression: Use a regular expression (regex) to identify a numeric value in the string and convert it to a float value. Define below. See also the example.

Regular Expression

This setting is only visible if you enable Extract Number Using Regular Expression above. Enter a regular expression to identify the numeric value that you want to extract from the string returned by the SNMP object at the specified OID. You can use capturing groups here.

Make sure that the expression returns numbers only (including decimal and thousands separators). The result is further refined by the settings below.

This setting is only visible if you enable Extract Number Using Regular Expression above. If your regex uses capturing groups, specify which one is used to capture the number. Enter an integer value or leave the field empty.

Decimal Separator

This setting is only visible if you enable Extract Number Using Regular Expression above. Define which character is used as decimal separator for the number extracted above. Enter a string or leave the field empty.

Thousands Separator

This setting is only visible if you enable Extract Number Using Regular Expression above. Define which character is used as thousands separator for the number extracted above. Enter a string or leave the field empty.

Sensor Display

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel is always displayed below the sensor's name. The available options depend on what channels are available for this sensor.

You can set a different primary channel later by clicking the pin symbol of a channel on the sensor's Overview tab.

Graph Type

Define how different channels are shown for this sensor:

Show channels independently (default): Show a graph for each channel.

Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This generates a graph that visualizes the different components of your total traffic.This option cannot be used in combination with manual Vertical Axis Scaling (available in the channel settings).

Stack Unit

This field is only visible if you enable Stack channels on top of each other as Graph Type. Select a unit from the list. All channels with this unit are stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Inherited Settings

By default, all of the following settings are inherited from objects that are higher in the hierarchy and should be changed there if necessary. Often, best practice is to change them centrally in the Root group's settings. For more information, see section Inheritance of Settings. To change a setting for this object only, disable inheritance by clicking the button next to inherit from under the corresponding setting name. You then see the options described below.

Select a scanning interval (seconds, minutes, or hours). The scanning interval determines the amount of time that the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations.

If a Sensor Query Fails

Define the number of scanning intervals that the sensor has time to reach and check a device again in case a sensor query fails. Depending on the option that you select, the sensor can try to reach and check a device again several times before the sensor shows a Downstatus. This can avoid false alarms if the monitored device only has temporary issues. For previous scanning intervals with failed requests, the sensor shows a Warning status. Choose from:

Set sensor to down immediately: Set the sensor to a Down status immediately after the first failed request.

Set sensor to warning for 1 interval, then set to down (recommended): Set the sensor to a Warning status after the first failed request. If the following request also fails, the sensor shows an error.

Set sensor to warning for 2 intervals, then set to down: Set the sensor to a Down status only after three consecutively failed requests.

Set sensor to warning for 3 intervals, then set to down: Set the sensor to a Down status only after four consecutively failed requests.

Set sensor to warning for 4 intervals, then set to down: Set the sensor to a Down status only after five consecutively failed requests.

Set sensor to warning for 5 intervals, then set to down: Set the sensor to a Down status only after six consecutively failed requests.

Sensors that monitor via Windows Management Instrumentation (WMI) always wait at least one scanning interval before they show a Down status. It is not possible to immediately set a WMI sensor to a Down status, so the first option does not apply to these sensors. All other options can apply.

If you define error limits for a sensor's channels, the sensor immediately shows a Down status. No "wait" option applies.

If a channel uses lookup values, the sensor immediately shows a Down status. No "wait" options apply.

Schedules, Dependencies, and Maintenance Window

You cannot interrupt the inheritance for schedules, dependencies, and maintenance windows. The corresponding settings from the parent objects are always active. However, you can define additional settings here. They are active at the same time as the parent objects' settings.

Schedule

Select a schedule from the list. Schedules can be used to monitor for a certain time span (days or hours) every week.

You can create schedules, edit schedules, or pause monitoring for a specific time span. For more information, see section Account Settings—Schedules.

Schedules are generally inherited. New schedules are added to existing schedules, so all schedules are active at the same time.

Maintenance Window

Specify if you want to set up a one-time maintenance window. During a maintenance window, the current object and all child objects are not monitored. They are in a Pausedstatus instead. Choose between:

Not set (monitor continuously): No maintenance window is set and monitoring is always active.

Set up a one-time maintenance window: Pause monitoring within a maintenance window. You can define a time span for a monitoring pause below and change it even for a currently running maintenance window.

To terminate a current maintenance window before the defined end date, change the time entry in Maintenance Ends to a date in the past.

Maintenance Begins

This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.

Maintenance Ends

This field is only visible if you enable Set up a one-time maintenance window above. Use the date time picker to enter the end date and time of the maintenance window.

Dependency Type

Define a dependency type. You can use dependencies to pause monitoring for an object depending on the status of a different object. You can choose from:

Use parent: Use the dependency type of the parent object.

Select a sensor: Use the dependency type of the parent object. Additionally, pause the current object if a specific sensor is in a Down status or in a Paused status caused by another dependency.

Master sensor for parent: Make this sensor the master object for its parent device. The sensor influences the behavior of its parent device: If the sensor is in a Down status, the device is paused. For example, it is a good idea to make a Ping sensor the master object for its parent device to pause monitoring for all other sensors on the device in case the device cannot even be pinged. Additionally, the sensor is paused if the parent group is paused by another dependency.

To test your dependencies, select Simulate Error Status from the context menu of an object that other objects depend on. A few seconds later, all dependent objects are paused. You can check all dependencies under Devices | Dependencies in the main menu bar.

Dependency

This field is only visible if you enable Select a sensor above. Click the Search button and use the object selector to select a sensor on which the current object will depend.

Dependency Delay (Sec.)

This field is only visible if you enable Select a sensor above. Define a time span in seconds for dependency delay.

After the master sensor for this dependency comes back to an Up status, monitoring of the dependent objects is additionally delayed by the defined time span. This can help avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Enter an integer value.

This setting is not available if you set this sensor to Use parent or to be the Master sensor for parent. In this case, define delays in the parent device settings or in its parent group settings.

Define the user groups that have access to the selected object. A table with user groups and types of access rights is shown. It contains all user groups from your setup. For each user group, you can choose from the following access rights:

Inherited: Use the access rights settings of the parent object.

None: Users in this group cannot see or edit the object. The object neither shows up in lists nor in the device tree. Exception: If a child object is visible to the user, the object is visible in the device tree but it cannot be accessed.

Read: Users in this group can see the object and review its monitoring results.

Write: Users in this group can see the object, review its monitoring results, and edit its settings. They cannot edit access rights settings.

Full: Users in this group can see the object, review its monitoring results, edit its settings, and edit access rights settings.

You can create new user groups in the System Administration—User Groups settings. To automatically set all objects further down in the hierarchy to inherit this object's access rights, set a check mark for the Revert children's access rights to inherited option.

If you want to extract a number in the response string using a regular expression (regex), note that the index for captures in this sensor is based on 1 (not on 0). Furthermore, capturing groups are not automatically created. The example below illustrates this issue.

Consider the following string as returned by a request for CPU usage:

5 Sec (3.49%), 1 Min (3.555%), 5 Min (3.90%)

Assuming you would like to filter for the number 3.555, this is the percentage in the second parentheses. Enter the following regex in the Regular Expression field:

(\d+\.\d+).*?(\d+\.\d+).*?(\d+\.\d+)

As Index of Capturing Group, enter 3. This extracts the desired number 3.555.

The index has to be 3 in this case because the capturing groups here are the following:

Group 1 contains 3.49%), 1 Min (3.555), 5 Min (3.90

Group 2 contains 3.49

Group 3 contains 3.555

Group 4 contains 3.90

Keep in mind this note about index and capturing groups when using number extraction.

It is not possible to match an empty string with the PRTG regex sensor search.

To change display settings, spike filtering, and limits, switch to the sensor's Overview tab and click the gear icon of a specific channel. For detailed information, see section Sensor Channel Settings.